Detailed studies have been initiated to identify the LDL receptor binding site on apoB-100. The complete amino acid sequence of apoB-100 has been analyzed by computer analysis. Several positively charged domains complementary to the negatively charged consensus LDL receptor binding domain have been identified on apoB-100. The presence of several potential binding domains rather than a single receptor binding domain provides new insights into the apoB-100 LDL receptor interaction. ApoC-II has been shown to be synthesized as a preproapolipoprotein. ProapoC-II undergoes proteolytic cleavage with loss of a hexapeptide to yield mature apoC-II. The predominate isoform in human plasma is proapoC-II, and mature apoC-II is a minor isoform in human plasma. Human apoA-I and apoB have been shown to be acylated with palmitate, and the fatty acid is linked to the apolipoprotein by an ester linkage. The identification of covalently bound fatty acids on apolipoproteins may be of pivotal importance in our understanding of lipid-protein interactions as well as apolipoprotein-lipoprotein metabolism. A processed form of apoA-I which has been cleaved at the carboyl-terminal region has been identified, and its structure established. The processed form of apoA-I is catabolized at a rapid rate in man and may provide major new insights into our understanding of the rapid catabolism of apoA-I in Tangier disease.